Effect of vacuum manipulation on inter laminar shear strength and flexural strength in double bag vacuum infusion moulding

The aim of this work was to gain insight towards the effect of vacuum manipulation on quality of the laminate by employing an additional bag over the first bag. First (inner) bag is used to infuse resin while second (outer) bag is connected with vacuum pump for compaction process only. Carbon fiber was used as reinforcement while epoxy was used as resin. Effects were related with compaction pressure and volatile management during infusion process. In this study a comparison is also presented between samples manufactured with vacuum infusion moulding employing single and double bag. Two schemes of vacuum manipulation inside the cavities (inner bag and outer bag) were introduced in the manufacturing setup of double bag vacuum infusion moulding (DBVI). Effect of varying vacuum applied levels was related to mechanical properties of the laminates. Samples were manufactured by keeping constant vacuum in the inner bag cavity while varying the same in the outer bag cavity and vice versa. Inter Laminar Shear Strength (ILSS) and flexural strength were used for evaluation process as both of them are critical indicators to assess quality of infused laminates. Testing as per ASTM standards along with image analysis were used for investigation of results. The results showed that employment of double bag, improved the properties under consideration as compared to samples manufactured using single bag. It was found that vacuum manipulation in these two bags can improve the mentioned properties. This improvement in properties was related with volatile management and compaction of fiber in dry and saturated conditions. Finally, a specific combination of vacuum inside the two cavities was also suggested in order to obtain improved properties.